1. Field of the Invention
The present invention relates to a digital echo cancellation device, and more particularly, to a digital echo cancellation device having improved convergence with a small amount of calculation and a small amount of memory.
2. Description of the Related Art
In the field of high speed communication applications such as asymmetric digital subscriber's line (ADSL), echo is common communications problem. Therefore, research has been conducted regarding apparatuses and technologies for removing echo.
A conventional echo cancellation device is disclosed in U.S. Pat. No. 4,268,727, entitled “Adaptive Digital Echo Cancellation Circuit,” registered on May 19, 1981, and issued to Agrawal et al. FIG. 1 is a block diagram showing the structure of the digital echo cancellation device disclosed in U.S. Pat. No. 4,268,727. Referring to FIG. 1, the conventional digital echo cancellation device includes a finite impulse response (FIR) filter and a correlator 32 for compensating for the coefficient of an adaptive filter using a correlation between a receive signal 102 and a send signal 104.
However, in the conventional digital echo cancellation device, many taps are required since the conventional digital echo cancellation device is constituted of an adaptive FIR filter and it takes a long time to obtain the optimal resolution since a least mean square (LMS) algorithm is used for compensating for the filter coefficient. In particular, when signals, in which a high correlation exists between each other, such as aural signals are input, convergence deteriorates and time spent on canceling echo increases.
Another conventional technology for solving the above problem is disclosed in U.S. Pat. No. 5,084,865, entitled “Echo Canceler Having FIR and IIR Filter for Canceling Long Tail Echos,” registered on Jan. 28, 1992, and issued to Koike. FIG. 2 is a block diagram showing the structure of a digital echo cancellation device, disclosed in U.S. Pat. No. 5,084,865. Referring to FIG. 2, another conventional digital echo cancellation device includes an FIR filter 6 and a tail canceler 7, which are connected to a hybrid 1. The tail canceler 7 includes an infinite impulse response (IIR) filter 24. After delay signals pass through the tapped delay line of the FIR filter 6, they are repeatedly multiplied with each other by the multiplier 14 of the IIR filter 24, and a correlator 22 compensates for the filter coefficient.
In the above digital echo cancellation device, the amount of calculation is reduced by using two-stage FIR and IIR filters, however, the stability of the output of the post-stage IIR filter deteriorates.